1. Field of the Invention
The present invention relates to an image processing apparatus and more particularly, to a method and apparatus for generating white color component and controlling the brightness in display devices.
2. Description of the Related Art
In a color display monitor or a color television, if a flat-panel display or color wheel filter is used, it is easier to increase the screen size, but the brightness of output image is deteriorated in comparison with use of a cathode-ray tube. To overcome such a drawback, a four-color output system in which white color component is added to the three primary colors of RGB (Red, Green, and Blue) is employed. The white component can be obtained by having a white light transmitted or reflected onto a white filter, which increases the overall brightness of the screen in display system. Therefore, what is needed is a method for extracting the white component from the RGB three primary colors to form the four primary color signals.
In an effort to increase the luminance of output image, a conventional method for using white filter in addition to RGB three color filters has been proposed by US-based Texas Instruments Inc., (U.S. Pat. No. 5,233,385). This method adopts a field-sequential way in which a white filter field or white frame is added by spatially or temporally dividing a color wheel or a video frame into four regions. As a result, the luminance of the output image can be increased in proportion to the size of the white field in image output systems. Such increase in luminance, however, signifies the increase of an achromatic color component, which causes color saturation of picture elements or pixels of an image to be reduced.
Another conventional method therefor has been presented by Japan-based Canon K. K., (U.S. Pat. No. 5,929,843). This method implemented by a binary liquid-crystal display includes the steps of extracting white component data from R, G, B color data, performing a pseudo half-tone process on the white component, and transmitting the suppressed white component to the display dot of RGB and White, in which case Red, Green, Blue and White are pixel units. The main feature of this method is in the non-linear conversion of the minimum value with the white component data obtained among the R, G, B color data, where non-linear models are gamma, offset, and scale. The above method contributes to turning the previous field-sequential based white color supplement into a pixel unit while adjusting the applied amount of white component depending upon a preset model. However, it raises a problem in that a decrease in color saturation with addition of white color fails to be noticed.